diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
index 42cfb1f9f98..5a47835024e 100644
--- a/src/backend/utils/sort/logtape.c
+++ b/src/backend/utils/sort/logtape.c
@@ -202,7 +202,7 @@ struct LogicalTapeSet

 	/* The array of logical tapes. */
 	int			nTapes;			/* # of logical tapes in set */
-	LogicalTape tapes[FLEXIBLE_ARRAY_MEMBER];	/* has nTapes nentries */
+	LogicalTape *tapes;	/* has nTapes nentries */
 };

 static void ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer);
@@ -518,8 +518,7 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
 	 * Create top-level struct including per-tape LogicalTape structs.
 	 */
 	Assert(ntapes > 0);
-	lts = (LogicalTapeSet *) palloc(offsetof(LogicalTapeSet, tapes) +
-									ntapes * sizeof(LogicalTape));
+	lts = (LogicalTapeSet *) palloc(sizeof(LogicalTapeSet));
 	lts->nBlocksAllocated = 0L;
 	lts->nBlocksWritten = 0L;
 	lts->nHoleBlocks = 0L;
@@ -529,6 +528,7 @@ LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset,
 	lts->freeBlocks = (long *) palloc(lts->freeBlocksLen * sizeof(long));
 	lts->nFreeBlocks = 0;
 	lts->nTapes = ntapes;
+	lts->tapes = (LogicalTape *) palloc(ntapes * sizeof(LogicalTape));

 	/*
 	 * Initialize per-tape structs.  Note we allocate the I/O buffer and the